An X-ray image sensor using a CCD, in place of an X-ray photosensitive film, has been widely employed as an X-ray diagnostic instrument for medical use. In such a radiation imaging system, two-dimensional image data by radiation is obtained as an electrical signal by use of a radiation detector that has a plurality of pixels, and an X-ray image is displayed on a monitor by processing the signal with a processor. A typical radiation detector has a configuration in which a scintillator is disposed on photodetectors arranged one-dimensionally or two-dimensionally, and incident radiations are transformed by the scintillator into light, and are detected.
In this type of radiation detector, a yield obtained when manufactured deteriorates proportionately with the enlargement of an image. As a solution to this problem, a technique is known in which a plurality of detecting elements are arranged to enlarge an image when a large-screen imaging device for use in taking a chest X ray, for example, is produced, as disclosed in JP 09-153606A. This publication mentions that the yield of each element is prevented from decreasing, and production costs are reduced by combining the elements of a light receiving screen smaller than an actual imaging screen together.